The present invention relates to a method of filtering beverages and chemical, pharmaceutical, or similar liquids by separating insoluble particles, including those having colloidal structures, out of the liquid, whereby various filter aid components are dosed to the untreated, i.e. showing cooler sludges, liquid (unfiltered matter) for forming a filter cake by deposition; thereafter, the solid matter particles retained in the filter cake after having been deposited are rinsed out and the filter aids as well as possibly added stabilizers are regenerated for reuse.
For the filtration of liquids, especially suspensions that contain solid matter, it is known to use in addition to the actual filter, for example the mechanical filter elements of a vessel filter, filter aids. In cases of suspensions containing a small amount of solid material, these filter aids are intended for facilitating the formation of a filter cake that is removable from the surface of the filter elements, or in cases of slimy solid matter, is intended to loosen up the very tight cake that is formed. The filter aids are added directly to the suspension that is to be filtered and are deposited to form a cake for the preliminary clarification of the unfiltered matter (deposition filtration). Common filter aids are cellulose, silica gel, diatomite, perlites, charcoal, wood dust, and similar materials. These filter aids work altogether physically-mechanically, and thus do not change the chemical composition of the liquid and are insoluble. During deposition of the filter aids, numerous capillaries are formed in the filter cake that are small enough to retain the solid material, but are also numerous enough to ensure an optimum permeability. Classical filters for the preliminary clarification are frame or vessel filters; the filter aids used in such filters are useless after being exhausted or used up, and must be thrown away and sanitized as waste.
In cases where this preliminary clarification (preliminary filtration) alone does not provide the high requirements with regard to quality, for example in the case of high-quality beverages such as beer or wine, including such requirements as so-called gloss quality or the biological preservability, there is provided in addition a final clarification, a so-called sterilization or degermination filtration. For this purpose, layer frame filters or plate-like arranged filter elements in vessel filters, filter layers that are covered on both sides in filter modules, and/or membrane filters are used. As raw materials for layer filters or filter sheets, organic and inorganic materials that are generally fibrous or granular are used, for example celluloses of wood, cotton, synthetic fibers, kieselguhrs, perlites, .alpha.-alumina, as well as kaolin. In this connection, kieselguhrs serve to increase the filtration activity and perlites serve for loosening the lamellar structure and hence to increase the pore volume or sludge volume. Since both of these materials are floury, they weaken the mechanical stability of the filter bed, so that in the case of pressure thrusts or surges, for example due to mistreatment or misoperation, the filter sheets, particularly in the case of sterilization filtration, can break through, thereby greatly impairing the quality of the filtration. For the sake of safety, frequently provided downstream of such filters, i.e. on the sterile side, are in addition sterile filters having a fine pore size and a real screening efficiency, for example membrane filters having limber or resilient materials. In order to reduce the environmental impact of the useless filter aids that result in large quantities from the heretofore known procedures, and that must be stored in dumps at considerable expense, procedures for prolonging the exposure times of these filter aids have become known. DE-OS 36 26 378 discloses a procedure for the deposition filtration of beverages, in accordance with which a chemically regeneratable filtering material of powdery alumina is used.
In the PCT application publication number WO86/05511, a procedure for the final clarification and stabilization of liquids containing polyphenols and/or proteins is described, where the liquid that is to be reclarified and stabilized is preclarified by means of a centrifuge, is then mixed with a mixture of filter aids that retains very fine sludge material and stabilizers that absorb polyphenols and proteins, whereupon this is transferred as a suspension into a device that is suitable for the retention of solid material. The solid material cake that is built up in this device is regenerated after the conclusion of the treatment of the liquid in order to recover the filter aids and the regeneratable stabilizing material. This is accomplished with a 1 to 2% hydrous NaOH solution at a temperature of 50.degree. to 60.degree. C. In so doing, the known filter aid components, namely diatomites, cellulose fibers and/or granules, for example polyamides, halogenated polyethylene and/or polypropylene, especially fluoridated polyethylene, are used.
With the known filtering agents used in this procedure, the filtration-active structure thereof changes so much during the chemical regeneration that the filtration characteristics are to a great extent negatively influenced and the permeability and filtration intensity of the filter aids change, so that after a certain time of exposure, disposal thereof is required. Another filtering procedure on the market uses a self-contained filter that comprises two covers and, depending upon the filtration capacity, has several filter elements. These filter elements could be shifted on lifting rods via a special lifting device. For the preliminary and/or final clarification, cellulose, perlites, diatomite, and synthetic fibers are used that can be flushed onto the horizontal filter elements with warm water. A regeneration is effected with chemical agents outside of the filtering device. Also with this known procedure, the used filter aids must, despite extended exposure time, be disposed of as waste at considerable expense.
EP 0 031 522 B1 discloses a procedure for filtering beverages, particularly beer, according to the precoat filtration process, according to which as filter aid an agent is used that fully or partially consists of fibers of practically pure silicic acid with a staple length of approximately 30 to 7000 .mu.m and a diameter of approximately 4 to 20 .mu.m. The silicic acid is gained by dry spinning hydrous silicate of sodium and treating the gained sodium water glass fibers for converting the sodium silicate into silicic acid with hydrogen ion containing acid or saline solutions. In so doing, a filter aid can also be used that contains fibers of silicic acid to which up to 50% by weight of fiber shortcut of organic fibers have been added.
DE-AS 10 10 058 discloses that for a procedure for making a filter aid for beer or the like, degreased aluminum plate-like powder is treated in hot water in such a way that it covers itself with a boehmite coat. An aluminum plate-like powder treated in this way is supposed to provide alone or in combination with guhrs or other filter aids an improvement of the biological quality and the gloss quality of beer or the like.
Proceeding from the state of the art according to the aforementioned PCT application WO86/05511, it is an object of the present invention to provide a method or procedure for filtering beverages and chemical, pharmaceutical, or similar liquids in the general way described above, according to which the filtering-active structure of the filter aid used is maintained during its regeneration, the filtering characteristics remain unchanged despite repeated use, and the environment-polluting disposal of the filter aid is eliminated.